Major economic losses in commercial swine nursery facilities are caused by diseases spread via the respiratory route. These include Streptococcus suis-related infections, Actinobacillus suis-related infections, Haemophilus parasuis related to Glässer's, Disease, Mycoplasma infections caused by Mycoplasma hyorhinis or Mycoplasma hyosynoviae, Actinobacillus pleuropneumoniae-related infections, Pasteurella-related infections cause by Pasteurella multocida, infections caused by Bordetella bronchiseptica, Erysipelothrix rhusiopathiae, Salmonella spp. including Salmonella cholerasuis and Salmonella typhimurium, Escherichia coli, swine influenza viruses, porcine reproductive and respiratory syndrome viruses (PRRSv) and disease caused by porcine epidemic diarrhea virus (PEDV). The majority of the mortality observed in these young pigs occurs between three and five weeks post-weaning for S. suis infections and between four and six weeks post-weaning for H. parasuis infections.
S. suis produces signs and/or symptoms including meningitis, polyserositis, arthritis, myocarditis, pericarditis and abortion. H. parasuis often produces an acute septicemia that leads to death. Additionally, the latter is an important component in the Porcine Respiratory Disease Complex. A. suis and the Mycoplasma species are common respiratory diseases of pigs that are transmitted by nose-to-nose contact. M. hyopneumoniae and M. hyorhinis both produce significant respiratory disease, whereas M. hyosynoviae more commonly causes arthritis resulting in lameness. B. bronchiseptica also results in a respiratory disease that is called atrophic rhinitis. P. multocida is another organism associated with atrophic rhinitis and that is spread via mucous membranes. Swine influenza virus and PRRS also produce significant respiratory diseases in pigs. PRRS is also associated with a reproductive syndrome causing abortion. On the other hand, the Salmonella species, E. coli and PEDV cause intestinal diseases that result in diarrhea that can kill neonates and young very quickly.
Attempts have been made to control clinical disease associated with all of the bacterial species, including S. suis, H. parasuis and A. suis, by antibiotic treatment, by controlled exposure to live organisms, and by vaccination using inactivated, parenterally-injected bacterial vaccines (bacterins). A currently accepted strategy for protecting weaned pigs entering this stage of production involves vaccination using appropriate bacterins at the standard time of piglet processing followed by revaccination at weaning. Such vaccinations utilize inactivated antigens that are administered either intramuscularly or subcutaneously (parenteral).
In commercial settings, sows and gilts are often already exposed to the diseases for which their offspring, especially neonatal offspring, will be susceptible. When sows or gilts are seropositive because of previous exposure or vaccination, they transfer lactogenic antibodies to their neonatal offspring, which may protect the neonates for a period of time. Unfortunately, such maternal antibodies often interfere with the neonate being able to produce their own antibodies if they are vaccinated at too young an age with a parenteral vaccine. Parenteral vaccination mainly stimulates the development of IgG and IgM antibodies.
In 1989, pork producers in the United States developed the Pork Quality Assurance program, a producer education and certification program to reduce the risk of animal health product residues in pork. In 2007, this program was enhanced and became known as Pork Quality Assurance Plus (PQA Plus®). One of the aspects of this program is to reduce the use of parenteral injections, especially in young pigs, helping to ensure the safety of food products.